1. Field of the Invention
The present invention relates generally to a viscous fluid coupling device. In particular, the present invention is concerned with a snap-in-place wiper of a viscous fluid fan clutch for a vehicle.
2. Statement of the Related Art
A thermostatically-controlled viscous fluid clutch assembly for driving and rotating a vehicle cooling fan is well-known. A multi-bladed fan is removably secured to a body of the clutch assembly. The fan and clutch assembly are installed between an accessory pulley of a vehicle engine (typically the water pump pulley) and a radiator. The clutch assembly drives the fan at high speeds close to input speed when cooling is required and permits the fan to rotate at low speeds when cooling is not required. Thermostatic control of the fan through the clutch assembly reduces the load on an engine and the noise caused by fan rotation, resulting in horsepower gain and improved fuel economy.
Generally, a clutch plate, housed within the clutch assembly, having lands and grooves is mated to the body having complementary lands and grooves. A pump plate separates a pair of internally-contained chambers, a receiving chamber and a collecting chamber, from a reservoir. Gates in the pump plate permit selective flow of a viscous fluid from the reservoir to the receiving chamber and into a shear zone between the lands and grooves of the body and clutch plate. Fluid shear in the lands and grooves transfers input torque from the clutch plate to drive the body and the attached fan.
When cooling is not required, gates in the pump plate are closed and the fluid in the shear zone is pumped into the receiving chamber. Orifices in the pump plate permit passage of the fluid from the receiving chamber into the reservoir. The removal of a majority of the fluid from the shear zone substantially reduces the shear between the clutch plate and the body, thereby substantially reducing the rotation of the fan.
It is well-known to provide wiper elements on a surface of the pump plate in communication with the receiving chamber. A wiper, which can be formed as a thin, flat element, is secured to the pump plate (usually by welding) adjacent each pump plate orifice. In other embodiments, a wiper may be formed by stamping a projection in a pump plate. As the wiper encounters fluid in the receiving chamber, an increase in fluid pressure occurs as the wiper creates a fluid dam. The increase in fluid pressure results in increased fluid flow through a pump plate orifice.
To further enhance the pumping ability of a wiper, it is well-known to provide a "scoop" end surface on a wiper. A scoop end surface is a curved or planar surface of the wiper positioned adjacent a pump plate orifice. The scoop surface often includes an inlet or "bay" portion which receives oncoming fluid in the collecting chamber and creates a fluid dam.
In conventional fan clutches, the assembly of a wiper to a pump plate requires two stations. First, a wiper is positioned on the pump plate at a selected location to provide the fluid dam effect. Second, pump plate enters a welding station wherein the wiper is welded to the pump plate. The welding operation increases the manufacturing costs of a pump plate and is time consuming.
The art continues to seek improvements. It is desirable that a viscous fluid fan clutch assembly include wipers mounted on a pump plate to provide the required fluid dam effect and decrease the time to pump fluid from the receiving chamber to the reservoir. Furthermore, it is desirable that a wiper for a pump plate be quickly and economically secured to the pump plate.